Synthesis and the optoelectronic properties of diarylethene derivatives having benzothiophene and n-alkyl thiophene units

Six new unsymmetrical diarylethenes having both benzothiophene and n-alkylthiophene units have been synthesized. The structures of diarylethenes 2a–6a were determined by single-crystal X-ray diffraction analysis. The results showed that the alkyl chain length had a significant effect on the optoelectronic properties of these diarylethenes, including photochromism, fatigue resistance, fluorescence and electrochemical properties. The long alkyl chains can increase the cyclization/cycloreversion quantum yields but decrease the absorption maxima of diarylethenes 1–6. The long alkyl chains can also induce a remarkable bathochromic shift for the absorption maxima of the closed-ring isomers 1b–6b both in solution and in PMMA film. All these diarylethene derivatives showed good fluorescent switching (quench to ca. 10%) in hexane. The emission intensities and the fluorescent quantum yields of diarylethenes 1–6 decreased gradually with the alkyl chain length becoming longer. In addition, cyclic voltammetry tests showed that the alkyl chain length had a remarkable effect on the electrochemical behaviors of these diarylethenes.